note
muba
<p><c>map</c> and <c>grep</c> can be an intimidating functions, but quite useful once you understand them.</p>
<p>Let's consider <c>grep</c> first, since this one is a little simpler to grasp — or at least, that was my experience. <c>grep</c> takes two arguments, the second being a list of elements to work with, the first being the work that you want to have done on that list. You can specify that as a BLOCK, a code reference, or just the name of a function. <c>grep</c> then loops over the list, aliasing <c>$_</c> to each element in turn, and calls the given piece of code. Then it returns every element for which the code returned a true value.</p>
<c>
my @numbers = (0, 0.5, 1, 1.5, 2, 2.5);
# Calling grep with a BLOCK:
my @integers = grep {int($_) == $_} @numbers;
print join(", ", @integers), " are integers.\n";
# Calling grep with a function name:
my @basket = ("apple", undef, undef, undef, "banana", "cherry", undef, "date");
print "The number of elements in \@basket is ", scalar(@basket), "\n";
my @basket_1 = grep defined, @basket;
print "The number of *defined* elements in \@basket is ", scalar(@basket_1), "\n";
</c>
<p>See what happens? <c>grep</c> returns the elements of the list you gave it, for which the piece of code returns true. The non-grep equivalents would be:</p>
<c>
my @numbers = (0, 0.5, 1, 1.5, 2, 2.5);
# Calling grep with a BLOCK:
my @integers;
for (@numbers) {
push @integers, $_ if int($_) == $_;
}
print join(", ", @integers), " are integers.\n";
# Calling grep with a function name:
my @basket = ("apple", undef, undef, undef, "banana", "cherry", undef, "date");
print "The number of elements in \@basket is ", scalar(@basket), "\n";
my @basket_1;
for (@basket) {
push @basket_1, $_ if defined;
}
print "The number of *defined* elements in \@basket is ", scalar(@basket_1), "\n";
</c>
<p>Now, <c>map</c> is pretty similar, except that it allows you to change the elements:</p>
<c>
my @numbers = 1..10;
my @times_ten = map { $_ * 10 } @numbers;
print join(", ", @times_ten), "\n";
</c>
<p>Of course, these are just the basics — the range of things you can do with them is astonishing. I hope this helps you along.</p>
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